Conventionally, a grease is used as the follower for an oily ballpoint pen, but this is disadvantageous in that, for example, the grease not only has insufficient quality and causes separation or becomes compatible with ink during storage at a high temperature or for a long period of time, but also due to its opacity, can be hardly distinguished from ink and gives the impression that writing cannot be performed any more even though some ink remains.
A conventional oily ballpoint pen in general comprises a solvent portion in which 90% or more is occupied by 2-phenoxyethanol and/or benzyl alcohol, and since the vapor pressure of such a solvent at 20° C. is 0.2 mmHg or less, the evaporation of the solvent from the rear end part of a pen is less of a problem.
In addition, the ink viscosity at 25° C. is from 3,000 to 20,000 mPa·s, and therefore splashing due to impact rarely occurs.
Accordingly, a conventional oily ballpoint pen has, as long as the inner diameter of the ink reservoir tube is 2.8 mm or less, a strong tube resistance and by the effect of surface tension, causes no leakage of the ink from the rear end part even when the pen is left standing with the penpoint upward or sideward, and a follower is not necessarily required.
If a follower is used for an oily ballpoint pen in which the inner diameter of the ink reservoir tube is 2.8 mm or less, the tube resistance increases and starving or splitting readily occurs due to following failure of the follower at low temperatures or during high-speed writing. A follower with good flowability is therefore in demand.
However, if a follower with good flowability is used, the follower is readily splashed due to impact on dropping.
Furthermore, when the pen is left standing with the penpoint upward, depending on the standing environment, a problem of reversal between the ink and the follower is liable to occur, or a phenomenon (dripping) wherein the follower extends in aging to wet the wall surface of the ink reservoir tube and in combination with the effect of gravity, drips down the wall surface of the ink reservoir tube, resulting in a decrease in the amount of the follower at the rear end part of ink, is liable to occur.
In the case where pseudoplasticity is imparted to increase the apparent viscosity during standing and decrease the flowability so as to decrease reversal or dripping of the follower when the pen is left standing with the penpoint upward, the amount of the follower attached to the wall surface increases at the time of consuming of the ink and the amount of the follower present in the rear end part of ink decreases considerably as the ink is consumed. As a result, in an extreme case, the follower is lost from the rear end part.
Also, as described above, since the apparent viscosity in the low shear rate region is high, starving or splitting due to following failure of the follower is readily caused at low temperatures or at high-speed writing.
In addition, when an air bubble is present or created inside the refill, the air bubble cannot be expelled from the rear end part of the follower because the apparent viscosity in the low shear rate region is high, and this gives rise to a problem such as starving or splitting. Furthermore, if the air bubble grows or the pen body is left standing at a high temperature, the follower may leak out from the rear end part of the ink reservoir tube due to the increase in the volume of the air bubble.
That is, when a follower is used for an oily ballpoint pen in which the inner diameter of the ink reservoir tube is 2.8 mm or less, it is difficult to achieve a balance among the followability of follower at low temperatures or during high-speed writing, the resistance on dropping, the reversing property in standing upward and the dripping property.
Also, problems incurred by the decrease in the follower amount at the rear end part of ink along with consumption of the ink, or by the remaining of an air bubble must be overcome.
The inner diameter of the ink reservoir tube of a ballpoint pen is set in many cases by taking account of various balances such as ink discharge amount at the ballpoint pen tip, writing distance, good or bad looking from the filled-ink length in appearance, and design of the pen, and in the case where a follower is required, a follower having physical properties appropriate for the inner diameter set of the ink reservoir tube is necessary.
On the other hand, as for the aqueous ballpoint pen, followers used in an aqueous ballpoint pen where ink is directly housed in an ink reservoir tube are disclosed in Japanese Examined Patent Publication (Kokoku) No. 6-33024, Japanese Patent Nos. 2,859,068 and 3,016,749, and Japanese Unexamined Patent Publication (Kokai) Nos. 7-216285, 8-183286, 9-76687, 11-42882, 2001-63272, 6-336584, 2000-177288 and 7-266780. These followers have a function of preventing volatilization of water from the rear end part, leakage of ink caused when the pen is left standing upward or sideward, and splashing of ink due to impact.
The disclosed followers for use in an aqueous ballpoint pen are surely usable as a follower of an aqueous ballpoint pen.
Also, the disclosed followers are supposed to be filled in an ink reservoir tube having an inner diameter of 2.8 mm or more and probably for this reason, a gelling agent for imparting a shear-thinning property is used as an essential component in most of these followers.
In the case of using an ink reservoir tube with strong tube resistance having an inner diameter of 2.8 mm or less, a problem arises by the effect of a gelling agent, that is, starving or splitting readily occurs due to following failure of the follower at low temperatures or during high-speed writing, the amount of the follower attached to the wall surface increases at the time of consuming of the ink, or the amount of the follower present in the rear end part of ink seriously decreases as the ink is consumed.
The present inventors have developed a nonaqueous ballpoint pen using, unlike conventional oily ballpoint pens, a solvent having a high vapor pressure, but found that a follower is necessary for the nonaqueous ballpoint pen ink using such a solvent having a high vapor pressure.
Also, for the above-described reasons, a follower having physical properties appropriate for an ink reservoir tube having an inner diameter of 2.8 mm or less is required.
Accordingly, the above-described follower for an aqueous ballpoint pen, which has been heretofore disclosed and is commonly used, was used for the nonaqueous ballpoint pen using a solvent having a high vapor pressure, which is currently under development. As a result, the follower could not be used as-is.
Under these circumstances, an object of the present invention is to solve those problems and provide a follower for a nonaqueous ballpoint pen, which can be used also for a nonaqueous ballpoint pen using a solvent having a high vapor pressure, is stable without undergoing separation even during storage at a high temperature or for a long period of time, prevents volatilization of ink by sealing the ink from the outer air, causes no problem in the followability of the follower at low temperatures or during high-speed writing even when the follower is mounted in an ink reservoir tube with strong tube resistance having an inner diameter of 2.8 mm or less, ensures resistance against impact on dropping, has low susceptibility to reversal between the ink and the follower due to a difference in gravity when the pen is left standing with the penpoint upward, is resistant to the phenomenon (dripping) wherein the follower drips in aging down the wall surface of the ink reservoir tube, and is less reduced in amount of the follower at the rear end part of ink as the ink is consumed. The object of the present invention also includes providing a nonaqueous ballpoint pen containing such a follower.